1. Field of the Invention
The present invention relates to a reversible thermochromic composition. More particularly, the present invention relates to a reversible thermochromic composition which develops fluorescent color of yellow, yellowish orange, orange, reddish orange, red, or the like under color-developing conditions, and turns colorless under non-color-developing conditions.
2. Related Background Art
Several reversible thermochromic compositions are known which are constituted of a solubilized mixture containing essentially a reaction medium for causing reversible electron exchange between an electron-donating coloring organic compound and an electron-accepting organic compound in a specific temperature range as disclosed in U.S. Pat. Nos. 4,028,118, 4,732,810, 4,865,648, 4,720,301, etc.
These disclosed reversible thermochromic compositions for developing yellow, orange, or red color are not satisfactory in practical use owing to insufficient color density, insufficient color brightness, and to residual color in a decolored state.